Effect of isocyanate chain extender on the structure and properties of the blends of poly(butylene terephthalate) and thermoplastic polyester elastomer

Abstract

The effect of diisocyanate chain extender (CE) additives on the change of molecular structural characteristics, rheological, and mechanical properties of the blends comprising of poly(butylene terephthalate) (PBT) and thermoplastic polyester elastomer (TPEE) obtained by reactive compounding in the melt and having different phase structure is studied. It is shown that addition of CE in the amount of 0.2 wt% to 1.25 wt% causes an increase in viscosity of polyester melts and solutions owing to the chain extension reactions and intermolecular cross-linking of macro-chains which occur in the melt. CE has a strong effect on the character of deformation curves at straining of both polyesters in primary form and their blends irrespective of the ratio of components in them (phase structure of materials). At the increase of its concentration, values of high and low flow limits increase and the difference in values of these parameters decreases, that is, a sharp yield point is gradually degenerating. At the same time, increase in Charpy impact strength on notched specimens is observed, including the subzero temperatures range (−40°C). Besides, CE has an effect on crystallizability of both individual polyester components and their blends. The general trend (irrespective of the polyester type and phase structure of the blend) is the decrease in crystallization temperature. This fact is explained by limitation of molecular mobility due to an increase in the molecular weight of polyester and intensification of interchain interactions.